Posted
by
timothyon Friday January 15, 2010 @08:42PM
from the whoooshing-sound dept.

Unequivocal writes "Chalk another one up to Jules Verne. Physicist John Hunter is proposing a space cannon with a new design idea: it's mostly submerged. 'Many engineers have toyed with the [space cannon] concept, but nobody has came up with an actual project that may work. Hunter's idea is simple: Build a cannon near the equator, submerged in the ocean, hooked to a floating rig ... A system like this will cut launch costs from $5,000 per pound to only $250 per pound. It won't launch people into space because of the excessive acceleration, but those guys at the ISS can use it to order pizza and real ice cream.' Though it won't work on people, with launch costs that low, who cares?"

It'll always be more expensive to send people up, at least in the near term, but we will need to send up a lot of other things that could be done in unmanned launches using this or another innovative technology. Ideas such as this could work; it's merely an engineering problem at this point.

For example, building a skyscraper 2km tall is merely an engineering problem. A space elevator is merely an engineering problem. A script to automatically discard redundant comments is merely an engineering problem.

There are still a few engineering challenges left to making one though. For one thing we need a big counterweight, and the 'easiest' way to do that is to tow an asteroid into Earth orbit. I'd say building a space tug is an engineering challenge.

For one thing we need a big counterweight, and the 'easiest' way to do that is to tow an asteroid into Earth orbit. I'd say building a space tug is an engineering challenge.

I don't think towing an asteroid is the easiest way; it would be much easier to just start with a very small counterweight (e.g. a rocket stage, or even nothing). That would give you a very low-payload-capacity cable. No problem, you send a very small/light elevator-car up the cable, and when it gets to the end of the cable, it stays there and becomes part of the counterweight. Now you send a slightly larger/heavier elevator-car up the cable, and when it gets to the end, it stays there too. Repeat as necessary until you have enough mass at the end of the cable to support whatever payloads you want to bring up.

Even if a 1.5 light second long cable were feasible you'd still have to deal with the fact that, as far as I understand, the anchor would have to be in geosynchronous orbit. Since the Moon isn't in geosynchronous orbit, the surface moves relative to the Moon you'd end up winding the cable around the planet.

Even if a 1.5 light second long cable were feasible you'd still have to deal with the fact that, as far as I understand, the anchor would have to be in geosynchronous orbit. Since the Moon isn't in geosynchronous orbit, the surface moves relative to the Moon you'd end up winding the cable around the planet.

no, no! they would simply make the base of the elevator mobile, and put it onto a train that constantly runs around the equator at the speed of the earth's rotation, plus or minus (as appropriate) the speed of the moon's orbit.

1.26 seconds. That's less than the space between me and the car in front of me.

Please. The Moon drives around the Earth in a predictable orbit at the same speed. I'm fairly sure they're safe. Besides, nothing has happened yet for 4.53 billion years. Must be nice to have cheap insurance.

If this launcher is anchored at the surface, how will they compensate for the motion of the waves at the surface? Does that eventually become a non-issue due to the weight of the launcher?How would they 'catch' the cargo once it was launched into orbit?How rigid would such a structure need to be, and are there currents in the ocean that would cause bending stress issues between surface and the deepest parts of the structure?

If this launcher is anchored at the surface, how will they compensate for the motion of the waves at the surface? Does that eventually become a non-issue due to the weight of the launcher?

They don't need to worry about the wave motion because most of the structure is below the water. IIRC submarines on the surface don't really pitch and roll. The picture in TFA shows the structure rigidly connected to the control platform but probably that wouldn't be required.

Most reputable materials folks I know still claim its a fundamental technology problem, not merely a funding one. While the expected stresses are nominally within what an ideal carbon nano-tube structure can handle, the purity required for that is well beyond what we can manufacture.

In order to feasibly build a space elevator, we would need much improved nano-technology. Not that I feel that its necessarily an idea-killer -- I'm not terribly knowledgeable on nanotech, but its one of those fields that always surprises me with how fast its going.

Well, I can't claim credentials like yours, but lately I've thought that a launch loop [wikipedia.org] would be a much better idea than any of the gun or elevator ideas. It's gentle enough (~ 3g acceleration) to put people in orbit easily, requires no new materials, and supposedly could make multiple launches per day. Your thoughts?

Yes gents, Saddam Hussein could have given us cheap access to space ensuring new area of prosperity for mankind, and era of space colonization...and we killed him!

OR Saddam hired a quack who was assassinated before he was revealed to be a complete phoney.

Had there been something resembling a successful test, I'd say we may have screwed up, but the only mentioned test was a failure. Also I don't hold Saddam's judgment in very high regard, it doesn't sound like there was much peer review on this project, and the US tends to take useful technology and scientific talent from it's enemies rather than destroy it.

Therefore I doubt this was anything that would have been useful, but I suppose we'll probably never be able to verify or deny your conspiracy theory.

The man doesn't seem like a quack to me: http://en.wikipedia.org/wiki/Project_HARP [wikipedia.org]Also, the only mentioned test wasn't exactly a failure what I see; it just revealed some problems, which is understandable with such project.

The same principle works in multistage gas guns used in things like hypersonic shock tunnels and dynamic compaction of metal powder into solids. It works, but I get the impression that for military things explosives or rockets get the job done with less hassle.My undergrad thesis supervisor back then worked in the field and actually met this guy at a conference a year or two before he was assassinated.

I think anybody on Slashdot who refers to Saddam as the martyred hero of space travel is not being serious.

If Saddam had taken half the resources he put into exotic weapons and invested in his conventional forces, he'd be alive today — and probably the most powerful man in the Middle East. But training and equipping armed forces is hard work. A lot of dictators just can't be bothered. Instead they model themselves on the villains in James Bond movies: lots of parties, gloating, glitter, and top secret projects, but none of the dreary stuff that has to do with actual governing.

Depends on what you mean by exotic. If you mean nuclear, there's not much evidence. Well, there's evidence that Saddam put money into developing them, just no evidence that the money bought anything more complex than a centrifuge. There are, however, numerous documented examples of Iraq using chemical weapons, including some tests on their own population. Specifically, they are known to have had sarin, tabun and VX, and may have had others. He also put a lot of money into developing biological weapons [wikipedia.org].

Specifically, they are known to have had sarin, tabun and VX, and may have had others.

Well yes. We still have the receipts for some of those. But he didn't have them at the time. As to conventional forces... I don't think it would have made much difference. The USA had air support. Every time the Iraqis tried to put something in the air or looked like they might, the US blew it to pieces. And anyway, the Iraqi army was never defeated. They just took their uniforms off and the US is still fighting them.

OR Saddam hired a quack who was assassinated before he was revealed to be a complete phoney.

What does that remind me of.......

Doc: Of course, from a group of Libyan Nationalists. They wanted me to build them a bomb, so I took their plutonium and in turn gave them a shiny bomb case full of used pinball machine parts.

In all seriousness, Saddam only thought he had all of this doomsday projects in the works. The reality, which is supported by evidence apparently (from what I hear), is that most people working for Saddam were terrified of him and his sons and flat out lied or blew smoke up his ass about how far along they were with his ultimate weapons.

The only thing more tragically retarded and pathetic is the fact that a president and some intelligence agencies fell for the same bullshit. Or did they?:)

First of all, you can't get into stable orbit ballistically; you have to use a rocket motor at apogee of ballistic trajectory, at the least.

Also, we do have clear examples of electronics (from the 60's...) surviving launch to half of orbital velocity from a modified big naval cannon (Project HARP). And that's more or less a "normal" cannon, very short, very high acceleration. Look up V-3; such design can maintain almost constant acceleration, close to average one, and be hypothetically several kilometers long.

So why don't we go totally overboard, and assume a barrel length of 30km; and close to half of orbital velocity (so it will be easier, since there's ^2 in this part of equation;p) - 3.5 km/s. From simple calculations that gives 20 g. Definitely bearable, as far being launched from a cannon into space goes. With 5 km/s you have 42 g.

Yes, widely unpractical and even...stupid. But I didn't actually suggest using it for humans, just said that it might be almost bearable.

You are misinformed (and here you didn't even need to perform any basic calculations...)

http://en.wikipedia.org/wiki/G-force#Human_tolerance_of_g-force [wikipedia.org]Early experiments showed that untrained humans were able to tolerate 17 g eyeballs-in (compared to 12 g eyeballs-out) for several minutes// I would venture a guess they were breathing and their brain was supplied with blood// without loss of consciousness or apparent long-term harm. The record for peak experimental horizontal g-force tolerance is held by acceleration pioneer John Stapp, in a series of rocket sled deceleration experiments in which he survived forces up to 46.2 times the force of gravity for less than a second. Stapp suffered lifelong damage to his vision from this test//"this test" likely means eyeballs-out(emphasis mine)

In my hypothetical scenario with 20 g that acceleration would last only 17 seconds, quite bearable. In the overboard example with 42 g, it would last 12 seconds (eyeballs-in!), which still might be survivable (and with eyeballs-in, which stresses eyes less, perhaps even without long-term damage)

Seeing as ice cream is an emulsion if it gets warm enough it could fractionate into a much less tasty brew. However, if you keep ice cream very, very cold, it shouldn't be terribly affected by the g-forces if packaged properly. The real problem is what to do with real ice cream in an environment like the ISS where real ice cream can cause problems by virtue of the fact that loose fluids and crumbs need to be kept at a minimum for various reasons.

Actually there is very little in the way of supplies that could handle that acceleration. Maybe freeze dried soup, maybe water, but very little else. You wouldn't dare send gasses, electronics, whole foods (even canned) or replacement parts.

The whole idea hinges on the un-compressibility of water, making the extra long cannon easier to construct, but if you've ever seen a depth charge explode you know that only works so far. It also mentions an increase of pressure of 500% which is no where near enough.

This was short on details, but the military builds electronics into some bullets that function at 15,000 G's [wikipedia.org]. Napkin math says that would need a 1 mile long barrel to reach the 13k mph quoted in the article. if it was 5 miles long your 3500 G's you could launch about anything submerged in a liquid (typical wrist watch survives this without the liquid.) So about the only thing they couldn't launch is something living.But even at 1/2 mile their still under the accelertion of a gun, so wouldn't even deform

Make it long enough and it CAN launch people. (You'll need good streamlining to avoid nasty deceleration when it leaves the muzzle, though.)

The ocean is DEEP. Something that's roughly neutrally buoyant (i.e. a gun barrel supported by floats distributed along its length) needs to spend negligible structural strength supporting itself. (It only needs to be strong on any part that protrudes from the water - which might be a lot to avoid sinking it when it recoils.) You might want to put "helper combustion chambers" along it periodically to boost and smooth the acceleration if you want to launch live stuff though.

Also you can make it larger diameter and put sabots on the projectile while it's in the barrel to reduce the internal pressure variations or fire very dense loads. (Doesn't really help the materials strength issues, though, because the curvature lessens as diameter rises.)

A bit of math here. Escape velocity on earth is 10.735Km/sec, Acceleration at 6G = 9.8*6=58.8 M/Sec^2. 10735/58.8 = 182.5 Second to reach escape velocityDistance travelled during that that time 10.735*182.5/2 = 979 Km. Basically to accelerate a body to escape velocity with a steady 6G acceleration would require a tube almost 1000 KM long. Even popping up to 10G the tube would be 585Km long.

These calculations do not even take into consideration deceleration due to drag.

The reason space is expensive has more to do with the complexity of the rocket engines and the companies that build them than the propellant. If you want cheap access to space, focus on that. Capital-intensive projects that put heavy wear on their components (like guns) won't make things cheaper. The goal should be to *reduce* the number of parts that need maintenance.

It's so unfortunate that the press seems unwilling these days to dig even a *little* to get the story. Slashdot is linking to a blog, which is linking to Popular Science which is unwilling to even link to the company's website [quicklaunchinc.com] which has that tech talk embedded. It's like a 21st game of "telephone" and the message gets degraded at every retelling!

If you try to launch an object from the surface of the Earth using a "cannon" the projectile won't be doing anything other than decelerating throughout its flight and this means bringing the projectile to very high velocities where atmospheric heating and stresses become major problems. Then again, launch its self may be a problem as the Hydrogen propelling the projectile is detonating at an extremely high temperature and pressure. Small nitpick as well from TFA:

but those guys at the ISS can use it to order pizza and real ice cream.

A big reason space food is what it is instead of the Earthling food we're all accustomed to has to do with keeping the station reasonably clean and experiments doubly so. Crumbs and fluid loose in the station can cause problems.

The idea is to get something into orbit, not shoot it away from the planet. To go into orbit around Earth you have to fire the projectile with LESS than escape velocity.

If you just fire a projectile, with no rocket, into a non-escape orbit, the only possible orbits are those that intersect the firing point. That is, the projectile will go all the way around the planet and hit you from behind. You've just shot yourself in the back in the most dramatic way possible.

I think you dropped a zero or two somewhere in your calculation. Escape velocity from the Earth's surface (neglecting air resistance) is 7 mi/s. 7 mi/s * 60 * 60 = 25000 mph. Escape velocity is about twice the speed they're aiming for, plus you're going to burn a decent amount of that speed off in the atmosphere. Emphasis on "burn." Which makes perfect sense since they're talking about delivering payloads to Earth orbit, not to some solar orbit, which wouldn't be very useful.

Why launch pizza and ice cream, which might not withstand the 5000 G acceleration when you can launch a bunch of cubesats or microsatellites.
In fact there's a microsatellite(it's name escapes me) up there that's a web server. If you have some amateur radio equipment you can download and upload files to it. It can't store much, only enough for about an email or so.
But with improvements in electronics it'll be possible to store even more data on a microsatellite. So eventually the Pirate Bay or Wikileaks

These guys plan to have the gun propel the projectile to 6.0 km/s, and then the projectiles themselves are rocket motors that will add an additional 3.0 km/s. That gives them enough acceleration to reach orbital velocity and take into account friction/gravity losses.

The reason they plan to limit the gun to 6.0 km/s is because that requires the hydrogen gas to only reach 1700 kelvin, which after taking into account heat exchange with the barrel, it ends up being a few hundred kelvin below the melting point of steel ( the barrel ).

Yep. The only stable orbit that intersects the planet's surface is an escape hyperbola. An ellipse that does it once does it multiply. POW!

But by getting high enough above most of the atmospheric friction and having some dwell time there before falling back you've solved most of the problem. Circularizing the orbit (or at least raising the perigee above the atmosphere) is a minor job for a rocket motor compared to clawing its way up from a standing start while carrying the fuel for the whole launch.

I don't suppose the $250/lb launch costs include the build cost amortized over the lifetime of the system? Or the maintenance costs for that matter. The cost per pound on rockets includes those factors, and far too many people only work up the cost of electricity or whatever when working out the "launch cost" of one of these schemes.

In the end, once you've figured up the total cost of the system it's often more than just using rockets, even though rockets are so terribly inefficient.

If prices go from $5000/lb to $250/lb, demand for these launches will skyrocket (ha ha). If they launch often, maintenance and amortization costs can be shared by many clients, meaning they can keep the prices that low.

The launch costs might be based on an overly optimistic demand, though.

To fire it from a cannon the G force is going to be astronomically high. Very little is going to be able to survive that type of acceleration without massive damage. You could certainly fire a block of metal that fast without worry that it's ruined (though it will likely deform) but you put a 2 billion satellite in that and it's going to be absolutely destroyed by the acceleration. Even with a conventional rocket they spend several million dollars packing and testing the container the satellite is shoved in

To fire it from a cannon the G force is going to be astronomically high.

5000 G. That's about the equivalent of dropping something out a third-story window onto a concrete surface. Your laptop won't survive it, but bulk supplies (food, water, oxygen) will. Properly-designed equipment will as well: when your laptop hits the ground, it's not the computer chips themselves that break, but the joints -- electronic fuses in artillery shells don't have any trouble. You could even put entire satellites into orbi

Wow, that article is horrid. They don't even mention Hunter's startup company: Quicklaunch [quicklaunchinc.com]. On that page you'll find his Google Tech Talk on the subject which answers many of the questions that people are asking here.

Sorry, but I don't see the benefit of floating the cannon in the ocean. You have a very long structure that must be kept really close to perfectly straight that is subject to currents, waves, coriolis effects, etc. Worse, you are stuck with the projectile emerging into the densest part of the earth's atmosphere.

It would make a lot more sense to build a fixed structure on an appropriate, high mountain near the equator. Places like Peru or Ecuador come to mind as well as Mauna Kea on Hawaii. I'm sure there are more places that would be "developable" and logistically acceptable.

As some people have pointed out, most of the things you mention aren't problems. Loss of speed, straightness of barrel etc. Plus, as they say, you get to aim for different orbits in one platform

One thing they didn't point out which is significant: Logistics.

You go ahead and bring huge supply train up the side of Mauna Kea - I'm sure none of the neighbours will mind. As someone else pointed out, I'm sure they wont mind when something goes tits up and you send shrapnel towards them at a km/s.

The original Popular Science article [popsci.com] is a much better read and includes additional detail, including the fact that the projectile will experience 5,000G forces. Definitely not for human passengers.

Great, this could put a whole new light on lost baggage:
"Dear Mr. Jones. Your baggage was fired Tuesday. It should have arrived at the ISS before you did. Unfortunately, the capture system failed. The capsule has entered an unstable, atmosphere grazing orbit and will burn upon re-entry in about two weeks. We're sorry, but this loss is covered in the waiver you signed.
Sincerely,
A. Pratt"

I never cease to be amazed of some of the silly things that are published on Slashot.

A system like this will cut launch costs from $5,000 per pound to only $250 per pound. It won't launch people into space because of the excessive acceleration, but those guys at the ISS can use it to order pizza and real ice cream.

The ISS obital inclination is 56 degrees. Any 'ice cream delivery' made from a 0 degree inclination transfer orbit would have a relative velocity of about 7500 mph. The ice cream would effectively become an ASAT weapon.

Indeed. Although you could use the cannon to bring cargo + rocket engine to 13,000+ mph and use the engine to bring the cargo to the required velocity. This is of course assuming that you could solve the problem of high atmospheric and launch stresses and design a light, simple and robust engine for the final stage of the projectile's flight.

Basically, world record for rail gun right now is 5.5 km/s, after 200 million being spent on it. World record for Hydrogen gas gun is 11.2 at a fraction of the cost. Energy storage costs and other factors kill using electric for so large of a project.

He spends quite a bit of time discussing it when he goes over the history of rocket/guns, about 25mins in I think.

Also, he was paid by the navy to make gauss guns and rail guns, he just doesn't seem them as the right tool for this.

The real key demand for this technology is launching propellants to an orbital depot. The political climate has changed (temporarily I would say) so it's ok to talk about propellant depots again. ULA are doing some interesting research. [selenianboondocks.com] That's actual hardware being risk reduced there. Once you have propellant on-orbit you can plan deep space missions using Soyuz class vehicles - going beyond LEO doesn't need Saturn class launchers. That's the cost comparison that we have to look at.. not "is it cheaper